1. Field of the Invention
The present invention is broadly concerned with improved daily ration feed products for animals subject to heartworm infection including minor amounts of a heartworm preventative drug. More particularly, the invention is concerned with such feed products, and methods of preparing and using the products, wherein the feeds contain a sufficient quantity of a heartworm preventative drug so that when the animals consume the feeds, therapeutically effective amounts of the drug are established and maintained in the bloodstreams of the animals. In this way, conventional dosing regimes are eliminated, and the animals receive proper quantities of drug as a part of their normal daily diets.
2. Description of the Prior Art
Heartworm infection is an endemic condition with certain animals, and especially household pets such as cats and dogs. A number of drugs have been developed for the treatment of heartworm infection, such as the avermectins, which are a class of macrocyclic lactones. Drugs of this class include ivermectin, celamectin, moxidectin, milbemycin oxine and eprinomectin.
Ivermectin is a known oral and injectable medication used as a wormer, heartworm preventative and to kill certain mites (mange). Ivermectin is a mixture of (10E,14E,16E,22Z)-(1R,4S,5′S,6S,6′R,8R,12S,13S,20R,21R,24S)-6′-[(S)-sec-butyl]-21,24-dihydroxy-5′,11,13,22-tetramethyl-2-oxo-(3,7,19-trioxatetracyclo[15.6.1.14,8.020,24]pentacosa-10,14,16,22-tetraene)-6-spiro-2′-(perhydropyran)-12-yl 2,6-dideoxy-4-O-(2,6-dideoxy-3-O-methyl-αa-L-arabino-hexopyranosyl)-3-O-methyl-αa-L-arabino-hexopyranoside and (10E,14E,16E,22Z)-(1R,4S,5′S,6S,6′R,8R,12S,13S,20R,21R,24S)-21,24-dihydroxy-6′-isopropyl-5′,11,13,22-tetramethyl-2-oxo-(3,7,19-trioxatetracyclo[15.6.1.14,8.020,24]pentacosa-10,14,16,22-tetraene)-6-spiro-2′-(perhydropyran)-12-yl2,6-dideoxy-4-O-(2,6-dideoxy-3-O-methyl-αa-L-arabino-hexopyranosyl)-3-O-methyl-αa-L-arabino-hexopyranoside CAS: 70288-86-7.
Selamectin is identified as (5Z,25S)-25-cyclohexyl-4′-O-de(2,6-dideoxy-3-O-methyl-αa-L-arabino-hexopyranosyl)-5-demethoxy-25-de(1-methylpropyl)-22,23-dihydro-5-(hydroxyimino)avermectin A1a.
Moxidectin is SPIRO[11,15-METHANO-2H,13H,17H-FURO[4,3,2-PQ][2,6]-B ENZODIOXACYCLO-OCTADECIN-13,2′[2H]PYRAN-17-ONE]-6′-[1,3-DIMETHYL-1-BUTENYL]-3′,4′,5′,6,6′,7,10,11,14,15,17a,20,20a,20b-DIHYDRO-4′-[METHOXYIMINO]-5′,6,6,19-TETRAMETHYL-[6R-2aE,4E,4′E,5′S*,6R*,6′S*(E),8E,11R* 13R*,15S*,17aR*, 20R*,20aR*,20bS*]].
Milbemycin Oxime consists of the oxime derivatives of 5-didehydromilbemycins in the ratio of approximately 80% A4 (C32H45N07, MW 555.71) and 20% A3 (C31H43N07).
Eprinomectin is 4″-epiacetylamino-4″-deoxyavermectin B1 
These drugs are conventionally provided in tablet form or for larger animals as pastes and injectable liquids. Generally, animals are treated with relatively large doses of these drugs on a periodic basis. In the case of dogs and cats, tablets/chewables are given once a month by mouth year round for heartworm prevention. Higher doses are used to eliminate other parasites.
Ivermectin is the most commonly used heartworm preventative drug in domestic pets, and is generally considered safe at recommended dosage levels. If these are exceeded, side effects such as tremors, staggering, dilated pupils, loss of body weight or death may occur. As a consequence of normal dosing regimes for ivermectin, the treated animals necessarily receive a relatively large quantity of the drug which is to remain effective for an extended period. This in turn means that shortly after treatment the animal has a very high concentration of ivermectin in its bloodstream, with this concentration tailing off during the remainder of the period. This is to be contrasted with a more preferable treatment protocol wherein a substantially constant level of ivermectin is maintained on a continuing basis.
By the same token, the other established heartworm preventative drugs are generally administered in the same fashion as ivermectin, i.e., a relatively large quantity of the drugs are given at intervals, rather than daily administration of the drug to achieve a maintenance level in the animal's bloodstream.
U.S. Pat. No. 6,190,591 describes a single-extruder process for the production of controlled release particles which may be tableted. Various encapsulants including pharmaceuticals, nutraceuticals, nutritional compounds, biologically active components, flavorants, fragrances, detergents and surface-active compositions are described, at relatively large quantities in the particles of at least 1% and preferably from about 3-50%. Hence, the '591 patent is not concerned with complete feeds, but rather encapsulant particles. The process described in this patent make use of an elongated extruder where water and lipid are successively injected into the barrel, followed by water evaporation from the barrel and final addition of encapsulants. Such equipment is generally not suited to the production of a daily ration feed or similar product, given the need to uniformly distribute an active in the latter type of product.
There is accordingly a need in the art for improved feeds and methods of providing heartworm preventative drugs to animals in a manner which will avoid periodic, relatively large ivermectin doses and maintain a substantially constant level of ivermectin in the bloodstreams of the treated animals.